Unusual electronic properties and transmission in hexagonal SiB monolayers

After the success of graphene, several two-dimensional (2D) layers have been proposed and investigated both theoretically and experimentally in order to evaluate their structural stability and possible applications of these unusual materials in electronics. Except for graphene, only silicon and germanium were predicted to form semi-metallic honeycomb monolayers, while most of the binary graphene-like compounds are all semiconductors. These predictions have been corroborated for several 2D structures experimentally synthesized. Considering the possibility of finding other candidates in this realm, exhibiting exceptional electron mobility, we have explored low-dimensional silicon-boron compounds containing planar sp(2)-bonding silicon atoms, through first-principles density-functional theory calculations. We have demonstrated that the so-called h-SiB sheet, which is a structural analogue of 2D honeycomb binary compounds, exhibits good structural stability, compared to the structure of silicene, for example, and predicted that this structure is also able to roll up into thermally stable single-walled silicon-boron nanotubes. The h-SiB sheet exhibits a delocalized charge density like in graphene, but the partially filled pi band and two highest occupied sigma bands are above the Fermi level, leading to the metallic behaviour of this SiB sheet. In this sense, we perform first-principles electron transport calculations, based on the nonequilibrium Green's function formalism, which has demonstrated that h-SiB exhibits higher transmission around the Fermi energy than the transmission in graphene. Our results indicate the unusual conductivity of this new material and open up new possibilities for the realization of metallic graphene-like systems for electronic transport in low dimensions.